The present invention relates to a wire bonding apparatus and a wire bonding method for a semiconductor device, and more particularly, to a wire bonding apparatus and a wire bonding method for a semiconductor device which have been improved to heighten stability of bonding stress between electrodes of a semiconductor chip and inner leads.
The term xe2x80x9cwire bondingxe2x80x9d indicates connection between chip electrodes and inner leads in package assembling processes of semiconductor devices. For instance, chip electrodes, such as Al electrodes, on an electrode chip and tip end portions of Ag plated inner leads are connected by means of ultrafine wires, such as Au wires, by utilizing thermal energy (temperature atmosphere of 200 to 300xc2x0 C.) and ultrasonic energy; Auxe2x80x94Al alloys are formed by fusing Au balls at tip end portions of the Au wires with the Al electrodes and Auxe2x80x94Ag alloys are formed by fusing the Ag plated portions of the tip end portions of the inner leads with the Au wires.
FIG. 14 is a plan view of a wire bonding apparatus for a conventional semiconductor device and an arrangement similar to this is disclosed in Japanese Unexamined Patent Publication No. 326609/1993. FIG. 15 is a sectional view seen from the line XVxe2x80x94XV as indicated by the arrow in FIG. 14. In FIG. 14 and FIG. 15, a heat block 11 serves as a jig which is fitted between a heat block main body (not shown) and a lead frame 50 when performing wire bonding, and a lead frame forcing mold 13 is a jig for pressing the lead frame 50 from above to clamp the lead frame to the heat block 11.
The lead frame 50 is so arranged that a die pad 2, a hanging lead 8, a tie bar 9 and a frame 10 are successively formed. The hanging bar 8 is bent at portions proximate to four corner portions of the die pad 2 at which they are in successive communication and the die pad 2 is provided on a plane lower than a place on which the inner lead 4, tie bar 9 and frame 10 are provided (hereinafter, the die pad which is provided on a lower plane is referred to as a sunked die pad). The semiconductor chip 1 is joined to the die pad 2 through an adhesive 3.
The heat block 11 is so arranged that a die pad mounting portion 11a on which the die pad 2 is mounted is in the same plane as that of an inner lead mounting portion 11b onto which the inner leads 4 are mounted. The die pad mounting portion 11a is formed with vacuum suction holes 11c for closely adhering the die pad 2 thereby through vacuum suction. A square concave portion 11d is provided between the die pad mounting portion 11a and the inner lead mounting portion 11b so that close adhesion between the die pad 2 and the die pad mounting portion 11a is not hindered even when the handing lead 8 is deformed to extend below of the surface of the die pad mounting portion 11a upon adhesion of the die pad 2 to the die pad mounting portion 11a through vacuum suction. At four corner portions of the concave portion 11d, there are further formed grooves (not shown) which extend outward of the four corner portions so that the hanging lead 8 will not interfere with mounting of the lead frame 50.
A wire bonding method using a conventional wire bonding apparatus will now be explained. In performing wire bonding, the lead frame 50 is positioned and mounted on the heat block 11 as illustrated in FIG. 15, and after clamping by pinching the lead frame 50 between the frame forcing mold 13 and the heat block 11, the die pad 2 is fixed to the die pad mounting portion 11a through vacuum suction to perform wire bonding thereafter.
The hanging lead 8 which forms a part of the lead frame 50 is provided in the same plane as tip end portions 4a of the inner leads 4 and the sunken die pad portion is in the concave portion 11d formed between the die pad mounting portion 11a and the inner lead mounting portion 11b. A semiconductor chip 1 is mounted on the die pad 2 which is in successive communication with the hanging lead 8 through the adhesive 3 of, for instance, Ag paste.
The die pad mounting portion 11a and the inner lead mounting portion 11b are arranged on the heat block 11 such that they are formed in the same plane. In contrast thereto, in the case of mounting the die pad 2 of the lead frame 50 having a dimension of 0.20 mm as defined by the sunken die pad onto the die pad mounting portion 11a, the die pad 2 is pushed upward by 0.20 mm. Since the lead frame 2 might include manufacturing errors of, for instance, xc2x10.05 mm, the dimension of the lead frame 50 as defined by the die pad sinking is varied in the range of 0.15 mm to 0.25 mm whereas the die pad 2 is pushed upward by the same amount.
In this condition, the hanging lead 8 and the inner leads 4 are pinched and clamped between the heat block 11 and the lead frame forcing mold 13. The die pad 2 is then fixed onto the die pad mounting portion 11a by means of vacuum suction of a rear surface of the die pad 2 through the vacuum suction hole 11c whereupon the wire bonding process is started.
In the wire bonding process, while heat is applied to electrodes such as Al electrodes, though not shown in the drawings, which are provided at a specified electrode pitch on the semiconductor chip 1 and to tip ends of ultrafine Au wires 6 by means of the heat block 11, pressure welding is performed while applying ultrasonic vibration to the Au balls formed at the tip ends of the Au wires 6 through electric discharge to connect the Al electrodes and the Au wires 6. The Ag plated portions formed at the tip end portions 4a of the inner leads 4 and the ultrafine Au wires 6 are connected by applying heat through the heat block 11 and the frame forcing mold 13 while applying ultrasonic vibration to the ultrafine Au wires 6.
In such a conventional wire bonding apparatus of the above-described arrangement, when detaching the frame forcing mold 13 upon completion of wire bonding, the die pad 2 and the hanging lead 8, which had been forcibly deformed by means of the heat block 11 and the frame forcing mold 13, are released from clamped conditions the moment the frame forcing mold 13 is detached, whereupon the die pad 2 is restored and descends by an amount it had been pushed up and the Au wires 6 are forcibly extended by an amount they were pushed up, so that there is presented a drawback that tensile force is applied to the Au wires 6.
Further, in case manufacturing errors are present in the sunken die pad, there are presented drawbacks that deformation is applied to the hanging lead 8 arranged as to successively communicate with the die pad 2, so that in a following process of resin sealing (not shown), the Au wires 6 are exposed on the surface of the resin when position of the semiconductor chip 1 is varied in an upward direction, and that the die pad 2 is exposed on the surface of the resin in case the position of the semiconductor chip 1 is varied in a downward direction. Such phenomena remarkably occurred in case of packages of, for instance, TSOP (Thin Small Outline Package) type or TQFP (Thin Quad Flat Package) type of especially small thickness, e.g. 1 mm.
A drawback was further presented when the semiconductor chip 1 is uniformly joined to the die pad 2 having a size substantially identical to that of the chip by means of a bonding material. The uniformly joined semiconductor chip 1 and the die pad 2 exhibit deformations such as inclinations or bowing owing to a difference in coefficients of thermal expansion.
The present invention has been made for solving the above-described problems, and it provides a wire bonding apparatus and a wire bonding method for a semiconductor device capable of decreasing an amount of restoration of the hanging lead and decreasing tensile force applied to the wires at the time of detaching the frame forcing mold.
The present invention further provides a wire bonding apparatus and a wire bonding method for a semiconductor device preventing exposure of the Au wires on the surface of resin or exposure of the die pad on the surface of the resin even in the presence of manufacturing errors in the die pad sinking.
The present invention also provides a wire bonding apparatus and a wire bonding method for a semiconductor device capable of restricting deformation such as inclinations or bows owing to difference in coefficients of thermal expansion of the semiconductor chip and the die pad.
In accordance with a first aspect of the present invention, there is provided a wire bonding apparatus for a semiconductor device comprising a semiconductor chip, and a lead frame having a die pad to which the semiconductor chip is joined and a plurality of inner leads which are aligned along a periphery of the die pad at specified intervals, wherein the apparatus includes a heat block having an inner lead mounting portion for mounting the inner leads, a concave portion provided inward of the inner lead mounting portion and at least one supporting pad for mounting the semiconductor chip.
There is further provided a wire bonding apparatus for a semiconductor device comprising a semiconductor chip, and a lead frame having a die pad to which the semiconductor chip is joined, a plurality of inner leads which are aligned along a periphery of the die pad at specified intervals and a hanging lead in which die pad sinking has been performed proximate to outward of the semiconductor chip for supporting the die pad, wherein the apparatus includes a heat block having an inner lead mounting portion for mounting the inner leads, a concave portion provided inward of the inner lead mounting portion while forming a clearance between portions to which die pad sinking has been performed, and at least one supporting pad for mounting the semiconductor chip provided within the concave portion while forming a difference in elevation with the inner lead mounting portion.
The supporting pad is arranged to have vacuum suction holes for sucking the semiconductor chip.
The apparatus is so arranged that it further includes a lead frame forcing means for pinching and holding the lead frame at regions other than the die pad and tip end portions of the inner leads between the inner lead mounting portion and the lead frame forcing means.
In accordance with a second aspect of the present invention, there is provided a wire bonding method for a semiconductor device comprising a semiconductor chip, and a lead frame having a die pad to which the semiconductor chip is joined and a plurality of inner leads which are aligned along a periphery of the die pad at specified intervals, wherein the method includes the steps of mounting the inner leads on an inner lead mounting portion of a heat block, mounting the semiconductor chip on at least one supporting pad which is provided in a concave portion provided inward of the inner lead mounting portion, and pinching and holding the lead frame at portions other than the die pad and tip end portions of the inner leads between a lead frame forcing means and the inner lead mounting portion.
In a device wherein the lead frame includes a hanging lead in which die pad sinking has been performed proximate to outward of the semiconductor chip for supporting the die pad, the method further includes the steps of arranging a concave portion of the head block such that a clearance is formed between portions of the lead frame to which die pad sinking has been performed, providing the supporting pad such that a difference in elevation is formed between the same and the inner lead mounting portion, and pinching and holding the lead frame by means of the lead frame forcing means at portions other than the die pad and tip end portions of the inner leads.
The supporting pad is arranged to have vacuum suction holes for sucking the semiconductor chip.